gms | German Medical Science

Objective: The correct histological differentiation of oligodendrogliomas from diffuse astrocytomas is difficult and highly subjective in cases without typical morphological features. For grade IV gliomas it was recently shown that gene-expression based classification is better correlated to survival than histological classification (Nutt et al., 2003). The same might be true for low-grade gliomas.

Methods: We retrospectively analyzed 122 histologically classified “pure” astrocytomas WHO II (AII) (n=43) and WHO III (AIII) (n=79) by using comparative genetic hybridization (CGH). Molecularcytogenetic changes were correlated with the patients’ overall survival. Re-examination of the initial histology was independently done by two neuropathologists.

Results: Of 122 analyzed tumors, a total of 18% showed a combined or single chromosomal loss of 1p/19q (25.6% of AII, and 13.9% of AIII). A combined loss of 1p/19q was seen in 20.9% of AII and 8.9% of AIII. Single loss of 1p was found in 2.3% of AII and 3.8% of AIII, single loss of 19q was seen in 2.3% of AII and 1.3% of AIII. Overall survival was significantly longer in patients with combined or single losses at 1p/19q (70.78±4.56 vs. 36.59±4.69 months, p=0.0008). This significance was lost if grouped by WHO grade for AII (71.67±1.45 vs. 43.06±6.71 months, p=0.105), but remained significant for AIII (70.33±7.07 vs. 38.31±6.12 months, p=0.0234). Of these 22 tumors, only 8 (4 AII and 4 AIII) were histologically reclassified as oligodendroglioma (Oligo) or oligoastrocytoma (OligoA), respectively, due to classical histomorphological appearance.

Conclusions: 25% of astrocytomas WHO II and 14% of astrocytomas WHO III were found to harbor losses at 1p and/or 19q. Survival correlated with the loss of 1p/19q in grade III glioma, but this correlation lost its significance in grade II tumors. Molecularcytogenetic analysis is a significant complementation of histologic evaluation to improve the prognostic evaluation in high-grade glioma, but has to be interpreted restrainedly in low-grade glioma.